A Multi-Technique Approach for Measuring Melting of Iron-Rich Materials at Deep Earth Conditions

The melting curves of materials at high pressures represent a key physical property that controls various major phenomena throughout Earth's deep interior. In particular, recent investigations have brought increasing attention to the multi-scale heterogeneities of the core-mantle boundary, with discussion around the possibilities of partial melting and/or iron-rich chemically distinct domains in the region. A major challenge to assessing such interpretations lies in the difficulty of precisely constraining relevant high-pressure melting temperatures, leading to large uncertainties associated in part with disagreements among melt diagnostics and experimental techniques.

We have developed a multi-technique approach to measure the melting curves of iron-rich materials at high pressures (Dobrosavljevic et al. EPSL 2022). The approach combines results from two independent in-situ techniques - synchrotron Mössbauer spectroscopy, sensitive to dynamics of iron atoms, and synchrotron x-ray diffraction, sensitive to atomic positions. Rich data sets collected at beamlines 3-ID-B and 13-ID-D of the Advanced Photon Source finely sample the pressure-temperature space of the deep Earth and provide precise constraints on temperatures of melting and solid-solid phase transitions. In this work, we apply the approach to iron-rich materials of interest to Earth's core-mantle boundary and discuss implications for compositions and dynamics of heterogeneities in the region.